Climate change could have devastating consequences for much of the world's ecosystems, but at least one area might benefit. Ancient rain forests thrived during severe warming millions of years ago, helping to create today's species diversity.

56.3 million years ago, planet Earth was going through one of its hottest periods. Average temperatures were 3-5 degrees higher than they are today, and carbon dioxide levels in the atmosphere a whopping 2.5 times thicker than what we've got today. Both of those are fairly extreme, and it seems reasonable that life struggled during these times. But, at least in the rain forests, that wasn't the case at all.

This particular period of global warming was known as the Paleocene-Eocene Thermal Maximum. Around 56.3 million years ago, Earth's temperature started increasing, and it took only 10,000 years for carbon dioxide to reach such high levels. This remained the norm for the next 200,000 years. Despite these seemingly harsh conditions, many species thrived, as the diversity of rain forest species tripled during this period.

Although some plants went extinct, this was one of the most successful evolutionary periods in Earth's history, with multiple new species emerging to take their place. Based on preserved pollen samples, we find the earliest records of both the passionflower and chocolate plant families in this time period. So, whatever other negative consequences of global warming there might be, could modern climate change be a boon for the Amazon and other rain forests?

Klaus Winter, one of the researchers on the project, suggests there could be a crucial difference between ancient and modern global warming, and that's bad news for today's rain forests:

"It is remarkable that there is so much concern about the effects of greenhouse conditions on tropical forests. However, these horror scenarios probably have some validity if increased temperatures lead to more frequent or more severe drought as some of the current predictions for similar scenarios suggest."

Indeed, the steady moisture was key to the success of the ancient rain forests. That helped to sustain the tropical ecosystem during the ancient warming period. If today's global warming does indeed create drought conditions, as Winter suggests is a real possibility, then rain forests go right back to the brink of disaster.